Central nervous system (hereinafter referred to as “CNS”) disorders nowadays concern large sections of the population. In particular on account of the increase in elderly people, the numbers of patients are increasing continuously.
CNS disorders are a type of neurological disorder. CNS disorders can be drug induced; can be attributed to genetic predisposition, infection or trauma; or can be of unknown etiology. CNS disorders comprise neuropsychiatric disorders, neurological diseases and mental illnesses; and include neurodegenerative diseases, behavioral disorders, cognitive disorders and cognitive affective disorders. There are several CNS disorders whose clinical manifestations have been attributed to CNS dysfunction (i.e., disorders resulting from inappropriate levels of neurotransmitter release, inappropriate properties of neurotransmitter receptors, and/or inappropriate interaction between neu-rotransmitters and neurotransmitter receptors). Several CNS disorders can be attributed to a deficiency of choline, dopamine, norepinephrine and/or serotonin. Relatively common CNS disorders include or go along with pain, epilepsy or epilepsy-related syndrome, pediatric epilepsy or pediatric epilepsy-related syndrome, memory pre-senile dementia (early-onset Alzheimer's disease), senile dementia (dementia of the Alzheimer's type), micro-infarct dementia, AIDS-related dementia, Creutzfeld-Jakob disease, Pick's disease, Parkinsonism including Parkinson's disease, Lewy body dementia, progressive supranuclear palsy, Huntington's chorea, tardive dyskinesia, hy-perkinesia, mania, attention deficit disorder, anxiety, dyslexia, schizophrenia, de-pression, obsessive-compulsive disorders, and Tourette's syndrome.
Particularly, epilepsy is the most common CNS disorder, affecting about 1% of the population worldwide. Epilepsy describes a condition in which a person has recurrent seizures due to a chronic, underlying process. Epilepsy refers to a clinical phenomenon rather than a single disease entity, since there are many forms and causes of epilepsy. Using a definition of epilepsy as two or more unprovoked seizures, the incidence of epilepsy is estimated at 5 to 10 people per 1000. An essential step in the diagnosis and treatment of a patient with a seizure is to determine the type of seizure that has occurred. The main characteristic that distinguishes the different categories of seizure is whether the seizure activity is partial or generalized or unclassified.
For the general population there are approximately 20-70 new cases per 100,000 diagnosed each year with a 3-5% lifetime probability of developing the disease. The older established antiepileptic drugs (AEDs) phenytoin, carbamazepine, clonazepam, ethosuximide, valproic acid and barbiturates are widely prescribed but suffer from a range of side effects. Furthermore, there is a significant group of patients (20-30%) that are resistant to the currently available therapeutic agents. Since 1989 several new drugs have been launched, including felbamate, gabapentin, lamotrigine, oxcar-bazepine, tiagabine, topiramate, vigabartrin, zonisamide and levetiracetam. While many of new AEDs show improved efficacies and side-effect profiles, about 30% of patients with epilepsy remain untreated. There is clearly a need for improved medication.
Pain is one of the most common reasons for a patient to seek medical care and in consequence, pain results in a tremendous number of lost work days per year.
Pain is an unpleasant feeling often caused by intense or damaging stimuli, such as stubbing a toe, burning a finger, putting alcohol on a cut, and bumping the funny bone. The International Association for the Study of Pain's widely used definition states: “Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. Pain motivates the in-dividual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Most pain resolves promptly once the painful stimulus is removed and the body has healed, but sometimes pain persists despite removal of the stimulus and apparent healing of the body; and sometimes pain arises in the absence of any detectable stimulus, damage or disease.
Pain is the most common reason for physician consultation. It is a major symptom in many medical conditions, and can significantly interfere with a person's quality of life and general functioning. Psychological factors such as social support, hypnotic suggestion, excitement, or distraction can significantly modulate pain's intensity or unpleasantness.
In 1994, responding to the need for a more useful system for describing chronic pain, the International Association for the Study of Pain (.IASP) classified pain according to specific characteristics: (1) region of the body involved (e.g., abdomen, lower limbs), (2) system whose dysfunction may be causing the pain (e.g., nervous, gastrointestinal), (3) duration and pattern of occurrence, (4) intensity and time since onset, and (5) etiology.
This system has been criticized by Clifford J. Woo If and others as inadequate for guiding research and treatment. According to Woolf, there are three classes of pain: nociceptive pain (see hereunder), inflammatory pain which is associated with tissue damage and the infiltration of immune cells, and pathological pain which is a disease state caused by damage to the nervous system or by its abnormal function (dysfunctional pain, irritable bowel syndrome, tension type headache, etc.).
In nociceptive pain, the stimulation of the sensory nerve endings called nociceptors causes the sensation of pain. Such pain often occurs after injury or surgery. The pain signals are transmitted by the nociceptors to the brain. Often the pain is localised, constant and has an aching or throbbing quality. Once the damage to the tissue heals the pain usually resolves. Treatment with opioids may resolve nociceptive pain. Psychogenic pain is a pain disorder that is associated with psychological factors. Some types of mental or emotional problems can cause pain. They can also increase or prolong pain. Stomach pain is one of the most common types of psychogenic pain. People with this pain disorder actually have real pain. The diagnosis is made when all physical causes of pain are ruled out.
Neuropathic pain is caused by abnormalities in the nerves, spinal cord or brain and is a chronic type of non-malignant pain with an estimated prevalence of over 1% of the population. Optimizing pain relief in these patients is crucial in helping a patient regain control of his or her life. The most common cause of neuropathic pain is injury or dysfunction of nerves. Injury or dysfunction of peripheral nerves or nerves descending from the spinal cord results in disinhibition of nerve impulses at the spinal cord which in consequence results in pain. Neuropathic pain can also be centrally mediated, rather than peripheral, in conditions such as spinal cord injury and multiple sclerosis.
Neuropathic pain can therefore be divided into two further classes; peripheral neuropathic pain and central neuropathic pain depending on whether the peripheral or central nervous system is affected.
Inadequate treatment of pain is widespread throughout surgical wards, intensive care units, accident and emergency departments, in general practice, in the management of all forms of chronic pain and in end of life care. This neglect is extended to all ages, from neonates to the frail elderly. African and Hispanic Americans are more likely than others to suffer needlessly in the hands of a physician; and women's pain is more likely to be undertreated than men's. Therefore, it is needed to develop therapeutic measures for treating or alleviating pain.